Diego Costa
Diego Costa has only scored one goal in seven appearances for Spain. Getty

Chelsea striker Diego Costa has admitted he is yet to prove his worth for Spain after national team manager Vicente Del Bosque recently claimed he is "not happy" what he has done for his country to date. The 26-years-old striker, nevertheless, has thanked the boss for giving him a new chance to prove the doubters wrong after he missed the last call-ups in March and June due to poor form and recurrent hamstring issues.

Costa scored 20 Premier League goals for Jose Mourinho in his debut campaign at Stamford Bridge bus has failed so far to do that for Spain. He has scored just one goal in seven appearances for la Roja while last season his commitment to the national team was even put in doubt by Real Madrid's Sergio Ramos after he ruled himself out of games against Belarus and Germany in November 2014 citing injury – even though he had played a full game for the Blues just days before.

With Juventus star Alvaro Morata injured, Bosque decided to hand Costa a new chance with Spain after last week including him in the squad for the coming European Championship qualifiers against Slovakia on 5 September and Macedonia three days later. Nevertheless, the national team manager didn't hide his disappointment on 1 September with the striker's performance at national level by saying: "We count on his willingness and his interest to play for Spain. The rest of the team are going to try to try to make life better for him here. We can't be very happy with what he has done for us but I have seen him playing well for Chelsea in recent games and that why he has returned to the team."

Costa has now suggested that the manager is right to question his performances as he is aware that he "ought" to give something back to Spain.

He said: "Of course I feel that I owe the team, I haven't done anything yet. I have to repay the faith that has been placed in me. Maybe I have been a bit anxious but that's why it's important to play well now," Costa said during a press conference as quoted by AS. "I think what's missing is that I need to score more goals. Every time I'm getting better physically, I know I can give a lot more to the team and hopefully that will start right now."

Questioned whether he thought he wouldn't get called up again, he said: "Yes, that can happen at any time."

He said: "I know that if I'm not playing well and someone else is the gaffer won't call me up. I'm only thinking about being fit, coming here and playing. I hope that in these games everything will be better.

"Strikers need to score goals, that's what I've been lacking here. When I score, my confidence will be higher and everything will come together. We have very skilful players and I don't have any excuses, I have to do things better. I'm getting to know my teammates better and although the style is different for me there are great players here. I need confidence, adapting to this style is easy."